It doesn’t help that there is so much misinformation about this way of eating that can make us fearful. At almost every turn, we are told that keto is unhealthy and unsustainable. My doctors do not support my way of eating, but I take their comments with a grain of salt. Your husband my find the same if/when he consults with his doctor, depending on how well informed his physician is. Whenever I have concerns, I bring them to this forum. There are many individuals here who have a true passion for this way of eating and knowing the science around most everything related to it. I learn from them and appreciate their knowledge base.
I’ve been on clean keto just shy of three years. I’ve lost 75 lbs. but gained so many additional health benefits besides weight loss and appearance. My muscles and joints don’t hurt anymore. All the inflammation in my body is gone. My skin is better. (No lie, my husband’s fungal toenail that he’s had for over forty years completely went away and is beautiful and normal now.) Before keto, I used to walk like an old woman because my legs would hurt so badly. My knee would go right out from under me with no warning and it would almost take me down. People would ask me all the time if I was okay. Thirty years ago, I torn a groin muscle and it would flare often. Debilitating. I also had a fatty liver and A-fib; all of these things have resolved. More benefits than I can count, and the most amazing thing to me is that they are all due to my optimal internal health.
My advice; read a lot on this forum and post your questions and comments here. Scores of people are here to help and encourage. If your husband eats clean keto for a month or so, I suspect his T2D will resolve and he will feel better than he has in years. I agree that he should strive to eat less than 20 grams of carbs per day.